After the Fall of Reach, the Prophet of Truth discovered the location of Earth but withheld knowledge of this discovery from the Covenant and other high-ranking officials.[7] To attack the human homeworld, he ordered a Jiralhanae assault fleet to secretly assemble at Unyielding Hierophant station in the Tau Ceti System. The fleet would overwhelm Earth's defenses in a single decisive strike. This would serve as the initial stages of Truth's plan to elevate the Jiralhanae as the military command caste of the Covenant, as opposed to the Sangheili whom he believed were dangerously prone to disillusionment.[7][8]

The Fleet of Sacred Consecration was detected on its way to Earth, prompting a quiet dragging of available ships back to Earth all morning. They were later detected near Io as a series of Slipspace "whispers." Probes were sent to investigate, but shortly afterward the Covenant fleet reverted to realspace near Earth, just outside the killzone of the planet's Orbital Defense Platforms (ODPs). UNSC forces went to TACCON Alpha 2. Fleet AdmiralHarper ordered his battle group to attack, but quickly received new orders from Fleet Admiral Terrence Hood to fall back and defend the ODPs. Having expected an overwhelming enemy offensive in the style of the Battle of Reach, the relative weakness of the attack puzzled the defenders.[11]

The Assault Carriers converged on the battle cluster including Athens Station, Cairo Station and Malta Station. The ODPs opened fire as the enemy entered range. Covenant troops boarded the stations, intending to demolish them with an Antimatter Charge each. As each bomb was planted the Covenant withdrew. Athens and Malta were demolished in quick succession. Cortana, aboard Cairo, deduced the nature of the threat and John-117 was dispatched to prevent the same fate from befalling Cairo.[11]

Cortana directed the SPARTAN-II to the bomb's location in Cairo's fire control center. En route to the bomb, John-117 rescued Commander Miranda Keyes and allowed her to board UNSC In Amber Clad. The frigate departed Cairo to join the fray.[11]

“The carriers are breaking through sir, they're headed straight for the Cairo!”

— Fleet Admiral Harper

The two Assault Carriers began to break through toward Cairo. Cortana directed Cairo's MAC against Solemn Penance but the ship did not stop to engage and instead made directly for New Mombasa on the surface. Admiral Harper led the attack on Day of Jubilation and depleted its shields. Keyes volunteered to attack the carrier immediately, but Hood was unwilling to pit a single frigate against such a large target.[11]

John-117 and Cortana managed to capture and defuse the Covenant antimatter bomb aboard Cairo. Deciding to use the device to their advantage, and with Lord Hood's approval, the Spartan leapt out of an airlock holding onto the bomb, using only the initial explosive decompression for impulse. A flight of Longsword interceptors opened a breach in the carrier's hull and allowed the Spartan to plant the charge deep within the warship. The detonation destroyed the assault carrier, with John-117 barely escaping in time. Safe in the vacuum of space due to his MJONIR armor, John-117 then 'fell' to UNSC In Amber Clad and was rescued.[11]

Regret's carrier came to stop over New Mombasa in the East African Protectorate[12] and deployed troops into the city and the surrounding area. UNSC high command wished to discover why the Covenant were landing only in Mombasa, and John-117 was ordered to capture Regret for interrogation. The Spartan was deployed with marines and ODSTs in a trio of Pelicans from the UNSC In Amber Clad near the city, but the dropships were shot down by a Covenant Scarab in Old Mombasa. John-117 and the survivors regrouped and pursued the walker to NM 105E, and across the bridge to New Mombasa Sector B. The Scarab was eventually trapped and destroyed at the end of a canal. Covenant forces started to withdraw to the assault carrier for slipspace departure.[13]

Regret's means of escape took the UNSC by surprise. The carrier initiated a Slipspace jump while still over the city. The UNSC In Amber Clad quickly recovered John-117 and followed in the fleeing ship's wake. The slipspace rupture severely damaged the city[13] and generated an EMP. Many ODSTs had not yet landed when the carrier escaped and were caught in the EMP and blast. Drop pods were disabled in flight and plunged into uncontrolled freefall. They were scattered across the city.[14]

“The Covenant have found Earth. They own New Mombasa. Anyone that could've driven them off is dead, or gone. I'd say that makes for desperate times.”

— Edward Buck

Immediately following the slipspace event, the Prophet of Truth's Jiralhanae-led reinforcements arrived.[15] The Jiralhanae absorbed the handful of ships that remained from Regret's fleet, which by now were controlled by Regret's Jiralhanae, and deployed more troops into New Mombasa. Sangheili crews and infantry were killed as part of Truth's plan to place the Jiralhanae as the Covenant's primary warrior race.[7]

The battle spread over the globe in the following weeks. The diminishing fleets of UNSC remained to contest in Earth's orbit, but the Covenant continued to raid the surface in search of Forerunner artifacts. Most Covenant forces were concentrated in East Africa.[4]

The Forerunner dreadnought arrived at Earth on the 17th of November. John-117 left the ship by leaping off during re-entry and crashing into the East-African jungle.[19][21] On the ground, the Covenant had set up heavy defenses including several AA Batteries near Voi and in the surrounding area to protect their excavation of the Portal.

UNSC forces tracking John-117's descent.

Throughout the first several weeks, the fleets above Earth led by Fleet Admiral Harper fiercely fought the Jiralhanae-led covenant ships. However, on the 17th of November, Truth would arrive with the largest Covenant fleets in recorded history. Outnumbered and outgunned in every possible way the UNSC Home Fleet put up some of the fiercest resistance seen during the war. With nearly 300 ODPs and Hood's brilliant leadership, the UNSC destroyed hundreds of medium and heavy class Covenant ships, eventually reducing the massive fleet to no more than 40. In return, the UNSC fleet was entirely wiped out. Only a handful of frigates remained.[4]

During Spartan-117's re-entry, a pair of ODSTs used a laser designator during the Battle of Sector Six in Afghanistan to track the Spartan's fall.[22] The data made it easier for Sergeant Johnson and Thel 'Vadam to locate the Spartan. After several skirmishes with Covenant forces, Spartan-117 and the rest of the team was extracted by a dropship, and taken to Crow's Nest.[21]

“Marines, the Prophet of Truth doesn't know it yet, but he's about to get kicked right off his throne. You will take our city back and drive our enemy into the grave they've been so happily digging. One final effort is all that remains.”

With UNSC ground forces now supported by John-117, Commander Keyes proposed a plan to attack the excavation site by destroying several of the Covenant anti-air defenses at Voi, allowing low-flying frigates to strike the Anodyne Spirit now stationed on the Portal. Even though Fleet AdmiralTerrence Hood had only a few ships remaining, he agreed to the risky plan.[4]

As the offensive got underway the Covenant attacked Crow's Nest. The UNSC evacuated and detonated the base as it fell to Covenant forces. John-117, having activated the bomb, barely managed to escape.[4] The scattered UNSC forces regrouped along the Tsavo Highway headed for Voi.[23]

The Covenant AA gun was destroyed by UNSC and Separatist forces

At Voi, the UNSC successfully created a small opening in Covenant defenses. Throughout the assault John-117, with the help of Thel 'Vadam, disabled several AA Wraiths as well as one of the main AA batteries. With the way cleared, Admiral Hood ordered three frigates and multiple Longswords to attack the Anodyne Spirit. Despite direct hits from several MAC rounds, the Forerunner ship remained intact and activated the Portal. The Anodyne and the rest of the Covenant fleet departed through the resulting Slipspace portal.[24]

While the battle for Earth raged, the Covenant Separatist forces had been attempting to maintain a quarantine of the Flood-infested High Charity and Installation 05. The Flood-infested Indulgence of Conviction escaped and arrived at Earth as the Prophet of Truth departed through the Portal. The ship crashed in Voi and began infesting the area. John-117 and Thel 'Vadam quickly made for the crash site intending to overload the ship's reactor in the hope that the explosion would stop the Flood.[5]

Covenant separatists ships, led by Sangheili Fleet MasterRtas 'Vadum aboard the CAS-class assault carrierShadow of Intent, arrived in pursuit of the Flood ship. Informed by the Sangheili that Cortana was possibly on the ship, John-117 went in search for her in the crashed Flood-infested cruiser. John-117 found the small storage device containing the AI; he entrusted to 343 Guilty Spark for repairs and they were extracted by Phantom to Shadow of Intent. Meanwhile, the Flood infestation was destroyed after the Covenant Separatist fleet glassed most of East Africa.[5]

Admiral Hood and Commander Keyes joined John-117, Thel 'Vadam, and Rtas 'Vadum aboard Shadow of Intent where 343 Guilty Spark repaired Cortana's damaged storage device. The device contained only a message from the AI; it warned the Flood-infested High Charity was en route to Earth, but that beyond the Portal there was a solution to the Flood without firing the Halo Array.[5]

Admiral Hood was determined to make his stand against the Flood on Earth. The Sangheili believed this to be foolish for there was little hope that Earth could withstand a Flood invasion. The Sangheili decided to place faith in Cortana and journey beyond the Portal. John-117 and Keyes convinced a weary Lord Hood to allow them and a UNSC task force to accompany the Covenant Separatists.[5]

The Covenant had also been excavating and defending a site in Fort Huachuca, Arizona. After the departure of the Anodyne, the UNSC assaulted this site. Two days later, a nuclear bomb was detonated at this artifact. Finally, Operation: MARSH FLASH successfully removed high value Brute leadership attempting to activate the artifact there.[2]

“Before 2552, there was no way anything like that could happen on Earth. On one of those distant planets in the outer colonies, maybe. But an attack on Earth? Couldn't happen. Until it did. It's called glassing. Covenant warships rain plasma down on a planet until everything and everyone on the surface melts. Usually, it's complete world destruction. Earth only got a taste. The prolonged orbital bombardment destroyed East Africa, killing millions before it ended. None of us were safe anymore.”

Despite having suffered enormous military and civilian losses, the UNSC retained control of Earth. The battle and the war was over.

The Battle of Earth inflicted massive infrastructural damage to the planet and greatly reduced Earth's human population. The UNSC Home Fleet was left in ruins, and much of Earth's military power was destroyed. However, thanks to the defeat of the Covenant and the Flood at Installation 00, humans could now rebuild their homeworld, and re-expand.

Once through the Portal, the UNSC and Covenant Separatist forces would fight what remained of the Covenant Loyalists and of the Flood in what was known as the "Battle of Installation 00." In the battle, the Covenant Separatist fleet would crush what was left of Truth's fleet while on the surface, UNSC forces spearheaded by John-117, would stop Truth from firing the Halo Array. Gathering knowledge from the ruined city, the Flood would find the location of the Ark and crash its flood-infested High Charity on the Ark. Expecting to be safe from the Halo Arrays, the Flood would face both John-117 and Thel 'Vadam whom would eventually damage the Ark and reduce what remained of the Flood by activating the unfinished Halo Installation.[26]

There were a multitude of different smaller engagements during the Battle of Earth. The space around Earth was heavily contested throughout the battle. The skyhooks and Space elevators above Earth were also besieged.[27] On the ground, the cities of Mombasa, Cleveland, Havana, and Voi were all major battlegrounds during the battle. Sydney was also attacked.[28] Ross Island was also occupied by Covenant forces for some time. Sector Six in Pakistan also came under attack.

1412 Hours[1]: The Covenant launch waves of boarding craft toward the orbital defense stations. Several UNSC vessels and stations are destroyed by boarding Covenant forces. The MAC platform Malta, after sending elated communications that they have repelled all Covenant boarders, is annihilated in a cataclysmic explosion. The shockwave of which is felt by the crew of the Cairo station. Shortly afterward the Athens MAC platform experiences the same fiery fate.[11]

The Cairo MAC platform is saved by the heroic efforts of Spartan-117, single-handedly disarming (with the aid of Cortana who was acting as the platform's AI) and removing the Antimatter Charge from the orbital platform. John-117 removes the explosive device by jettisoning it, along with himself, out of a docking bay airlock. He then uses this same bomb to destroy a Covenant Assault Carrier that had just broken through the UNSC's defensive perimeter.[11]

During a protracted naval engagement, Solemn Penance blows through the Malta's debris field and heads straight for Earth.

Between 1459 & 2359 Hours[1]: Solemn Penance comes to rest above Mombasa. UNSC forces engage the Covenant on the ground and wage a bloody street-by-street skirmish in both Old and New Mombasa. After some time of ground battle and complete evacuation of Mombasa, SPARTAN-117, along with several Marines, are sent to crush the Covenant resistance in the city and infiltrate Solemn Penance above the city,[12] complimented by an ODST force which would be inserted from orbit directly into the Assault Carrier, though one squad's mission was actually separate.[14]Solemn Penance makes a sudden Slipspace jump only hundreds of meters above the city of New Mombasa. His motivations for doing so were, at the time, unknown. The Assault Carrier is followed by UNSC In Amber Clad. This atmospheric Slipspace jump severely damages the City of New Mombasa. The ODSTs' drop pods are scattered around the city, most of them presumably killed by the slipspace rupture.[14]

Immediately following the slipspace event, Truth's backup fleet arrives and engages UNSC forces in orbit. The Jiralhanae overtake the Sangheili on both the ground and in space while continuing to engage the UNSC. A Jiralhanae-led occupation force is also inserted into New Mombasa. The surviving UNSC and NMPD forces clash with the Covenant for control of the city.

Truth arrives at Earth with the largest Covenant fleet in recorded history. Truth's fleet smashes the UNSC Home Fleet, however in return taking massive casualties.[4] John-117 ejects from the Anodyne Spirit.[21]

Spartan 117 lands in Kenyan jungle. Later that morning, Spartan-117 is recovered by a group of Marines led by Sergeant Johnson. The Marines, with Spartan-117, make their way to Crow's Nest,[21] where a plan for a counterattack is devised. The base is invaded by the Covenant, and eventually destroyed by the UNSC.[4]

The UNSC forces regroup along Tsavo Highway, eventually assaulting the Covenant-held city of Voi.[23]

UNSC Forces neutralize Covenant Anti-Air defenses in Voi. Battle Group Victory initiate the assault on the Anodyne Spirit, with no effect. The Artifact is activated. Covenant Loyalist forces flee to Installation 00 through the Portal.[24]

Immediately thereafter, a Flood-controlled ship emerges from Slispace over Voi, crashing in the city.[24] The Flood infestation starts spreading around the region. Covenant Separatist fleet, having given chase, arrives at Earth and glasses Voi as well as its surroundings.[5]

A transmission from the UNSC AI Cortana is retrieved from the Flood ship. The Covenant Separatist forces, with several UNSC forces with them, go through the Portal to the Ark.[5]

At the beginning of the level Cairo Station, Admiral Hood remarks: "Something's not right. The fleet that destroyed Reach was fifty times this size."[11] Assuming that 'size' refers to the number of vessels in the fleet, this may be an oversight, as the Covenant fleet at Reach had only 300 ships, as opposed to the 750 (15*50= 750) implied by Hood's statement. The number of Covenant ships at Reach however has been revised to 750 in the 2010 edition of Halo: Fall of Reach but this was undone in the 2011 Definitive Edition. Since it is confirmed that more than one Covenant fleet was at Reach, it may be that Lord Hood was referring to the total number of Covenant ships present at the Fall of Reach, rather than just the Fleet of Particular Justice.

According to the Halo Encyclopedia, "the entire population of Earth was cut in half as the First Battle of Earth began." It does not however specify whether it means half of Earth's population were killed, or if a significant number were evacuated, although the latter is more probable, as the Covenant did not commence planetary bombardment, and the statement is in regard of the situation at the beginning and not the end of the battle.[31]

The Battle of Earth used to be regarded as separate battles, the "First" covering the events of Halo 2 and the "Second" the events of Halo 3. Later sources claimed Truth's reinforcements arrived mere hours after Regret fled, and the two battles were merged into one. However, the Halo Encyclopedia continues to list the two separate battles.

The Battle of Earth is featured in four games; Halo 2, Halo 3, Halo 3: ODST, and Halo: Spartan Strike, more than any other battle.

This is due to the fact that Earth, as Humanity's homeworld, is the most important planet under control of Humanity.